This invention relates generally to sheet feeding apparatus, and more particularly to an improved nip drive for an oscillating vacuum sheet feeder.
A typical apparatus in common use for feeding sheets is an oscillating vacuum feeder such as shown in U.S. Pat. No. 3,851,871, issued Dec. 3, 1974, to Aronson. In the apparatus of such patent, sheets are withdrawn seriatim from a stack by a ported oscillating cylinder coupled to a vacuum source. A sheet is vacuum tackled to the cylinder, with its ports in juxaposition with the sheet stack, and the cylinder rotates in a first direction to withdraw the tacked sheet from the stack and deliver the sheet into a sheet travel path. A pair of nip rollers, in juxtaposition with bearings supported on the cylinder, urge the withdrawn sheet, delivered into the nip, along the travel path. As the sheet is being urged along the path by the nip rollers, the cylinder rotates in the opposite direction to return to its position for withdrawing the next sheet from the stack.
While feeders of this type have proven generally effective in reliably removing sheets seriatim from a stack, each of the nip rollers must transmit equal driving forces on a sheet to avoid skewing of the sheet as it is transported along the travel path. In practice however, unequal driving forces are common due, at least in part, to the rigid interconnection provided between the nip rollers of such prior feeders.